1. Field of the Invention
The present invention relates generally to a method and apparatus for monitoring and controlling air pressure in pneumatic vehicle tires. More particularly, the invention concerns an improved apparatus for automatically checking tire pressure, checking for tire and system leaks, and for controllably inflating and deflating the tires as conditions warrant.
2. Discussion of the Invention
Various types of systems have been suggested in the past for controllably inflating and deflating vehicle tires during vehicle operation. Such systems typically include a source of air under pressure and controls for selectively increasing or decreasing an existing tire pressure, and for checking to determine the existing tire pressure for each tire. The ability to selectively increase or decrease tire pressure is desirable in connection with optimizing the operation of the vehicle under widely changing conditions including weather, vehicle load, terrain, and vehicle speed. Is also desirable to provide adaptability for isolating the air under pressure in each vehicle tire from the remainder of the system so that a problem such as a leak in one tire does not affect the air pressure in the other tires. Further, in connection with such a tire isolating feature, an air line from the system's source of air under pressure extends to a vehicle tire generally through the fixed axle upon which the tire and its associated wheel assembly are rotatably mounted and across a sealing arrangement between the fixed and rotating parts. The tire isolating valve is preferably between the sealing arrangement and tire so that the sealing arrangement is not subjected to system air under pressure other than at times of operation of the system to accomplish inflation, deflation or pressure checking.
Problems encountered in connection with prior art systems of the foregoing character, have included the inability to detect flat tires and to accurately obtain a predetermined desired tire pressure during inflation or deflation. Other problems have included the inability to achieve inflation or deflation from one tire pressure to another with accuracy and within a reasonable time period, and the inability to provide a system which is efficient in operation both from the standpoint of minimizing operator involvement and of obtaining both the required accuracy and the achievement of rapid inflating and deflating rates. A further problem with the prior art systems is to effectively prevent system failure due to contamination by rubber, dust and other contaminates routinely encountered during vehicle operation.
Efforts to improve accuracy have included the use of complex flow control valves and very slow flow rates of air between the source of air and the vehicle tires. However, such efforts undesirably result in the inability to achieve tire inflating or deflating within a reasonable time period. Moreover, complex flow control valves or valve arrangements are undesirably expensive both to manufacture and to maintain.
One of the most successful pressure monitoring systems ever devised is described in U.S. Pat. No. 4,782,878, issued to the present inventor. While this system was vastly superior to the prior art systems which preceded it, the system was not able to achieve the high levels of precision and control required in many applications as, for example, in certain military applications. Additionally, because the system was primarily analog based, the severe size and weight limitations required in many end-use applications made it inherently unable to provide the flexibility, versatility and accuracy desired.
For example, one aspect of the earlier system which contributed to a lesser degree of accuracy than is achievable by the present system is the fact that measurement of tire pressure in the earlier system was, of necessity, made immediately after the primary control valves were closed and before the system could fully stabilize. This requirement for measurement of the tire pressure prematurely and while the system was in flux resulted because the earlier system had no provision for stabilizing the system pressure prior to processing the transducer output signal. The prior system also lacked the important tire pressure equalizing feature which is present in the invention presently to be described. Absence of this feature further contributed to a lesser degree of overall accuracy.
Another important feature which is present in the present system but was lacking in the prior system relates to the ability of the apparatus of the present invention to detect both a flat tire and any system leakage. Such a feature is highly desirable if not mandatory from a vehicle safety standpoint.
Also absent in the prior system was the ability to properly accommodate high levels of particulate contamination. Field experience has shown that vehicles that are operated with variable tire pressure generate substantial rubber dust in the tires when the tire side walls are folding and unfolding. In fact, it is quite common to generate between one and two cups of this dust between tire changes. This pneumatic valve dust travels to the tire isolating valves and their operating mechanisms causing them to jam or stick. This serious problem is effectively solved in the apparatus of the present invention through a unique electronic modulation of all of the pneumatic valves. This modulation is of a character to create a controlled jarring action at the valves which effectively prevents valve poppet sticking and jamming due to particulate contamination.
There is also no provision in the prior art system for a variable inflate or deflate orifice which comprises an important element of reduction in inflate or deflate times optimized to the application and the apparatus. In the present device, modulation of all pneumatic valves provides the effect of a variable orifice and the frequency of modulation as controlled by the software programs of the system is utilized to achieve optimization.
In addition to providing superior accuracy, greater versatility, the ability to detect system leaks and the ability to accommodate high levels of particulate system, it will become apparent from the description which follows that the apparatus of the present invention also overcomes numerous other drawbacks found in the prior art systems.